ABSTRACT
Gas turbine output is a strong function of the ambient air temperature with power output dropping by 0.5% to 0.9% for every 1°C rise in ambient temperature (0.3%-0.5% for every 1°F). One way to counter this drop in output is to cool the inlet air. An approach becoming increasingly popular is that of the high pressure inlet fogging. Unlike conventional media type evaporative cooling, fogging can achieve 100% saturation of the air so that air can be cooled up to the wet bulb temperature.
In this paper, a thermodynamic analysis has been carried out for evaluating the gains from increased power and reduced heat rate of a gas turbine that results from pre cooling the turbine inlet air by inlet evaporative cooling and fogging. Both evaporative and fogging condition has been analyzed. For this analysis, two thermodynamic models have been developed; (i) an inlet evaporative cooling sub model (ii) a gas turbine performance sub model. Thermodynamic analysis of inlet evaporative cooling sub model predicts the cooled air temperature prior to the compressor. For the user’s convenience, thermodynamic analysis has been computer programmed using visual basics.
Gas turbine performance sub model, estimated from characteristic curves of heavy duty gas turbine and aero derivative gas turbine, predicts the resulting improvement in turbine power and heat rate and gives the expected hourly revenues. The results show that performance parameters indicative of inlet fogging effects have a definite correlation with the climate condition (humidity and temperature). In addition, this study indicates that the aeroderivative gas turbines, in comparison to the heavy duty industrial machines, have higher performance improvement due to inlet fogging effects. Plausible reasons for the observed trends are discussed.
